The present invention relates to an apparatus for changing the frequency of a dynamo engine, and more particularly to an apparatus for changing a frequency (for example 50 Hz) of alternating current to another frequency (for example 60 Hz), and vice versa, in accordance with a local commercial frequency.
The apparatus for changing the frequency is adapted to change the speed of an engine for the change of the frequency. Such an apparatus must be arranged to keep the output voltage of the generator constant in spite of the change of frequency. Japanese Utility Model Laid Open 58-108245 discloses an apparatus for changing the frequency of a dynamo engine. The apparatus has an operating lever which is manipulated by an operator to change the engine speed. More particularly, the operating lever is connected to a governor lever through a coil spring. When the operating lever is rotated a predetermined angle, the governer lever is rotated, so that a throttle valve of an engine is rotated to change the engine speed. At the same time, a switch for a generator is operated to keep the output voltage constant. The operating lever is rotated by switching of spring operating direction, when the lever passes the neutral point where the longitudinal direction of the lever coincides with the extending direction of the spring. However, there is no definite and sharp switching point at the neutral point, since the road of the spring is light, which means inferiority of operability.
In addition, since engine speeds for both frequencies are adjusted by adjusting the rotating angle of the operating lever, the rotating angle can not be set to a constant value. If the rotating angle becomes too large to operate the switch, a rated voltage can not be generated.